Michael Clarke Duncan never quite recovered from his July 13 heart attack – but he had his fiancée, Omarosa Manigault, by his side the whole time.

The former Apprentice contestant spent the last 50 days keeping vigil at his hospital bedside, a source tells PEOPLE. "She was literally there every second," the source says.

Adds the source: "She is a strong woman who is full of faith, but right now she is heartbroken."

According to the source, Duncan, who died at age 54 on Monday in Los Angeles, was already suffering major brain damage. The source also adds that doctors believe a second major cardiac episode is what killed him, but notes that his family had no intention of taking him off life support.

Manigault, meanwhile, sent a Tweet: "Thank you for your outpouring of love and support for my beloved Michael. ... He will truly be missed!"